Place bacon pieces in a large skillet and cook over medium-high heat, turning occasionally, until evenly browned, about 10 minutes. Drain on paper towels, leaving grease in the skillet.
Cook onion in the bacon grease in the skillet until translucent, about 5 minutes. Add Brussels sprouts and toss to coat in the bacon grease. Cook and stir until browned and tender, about 5 minutes. Stir in sugar, salt, and black pepper; sprinkle in bacon pieces.